swev-id: pytest-dev__pytest-5631 fix sentinel identity for WeirdEq (#10)

[casey-brooks]

Summary

• fix ValueError when collecting tests that patch an array #10 by ensuring sentinel detection only uses identity checks, avoiding ambiguous equality on numpy-like sentinels
• add a minimal regression test that patches os.path.abspath with a WeirdEq sentinel to reproduce the failure during collection

Reproduction snippet

from unittest.mock import patch


class WeirdEq:
    class Amb:
        def __bool__(self):
            raise ValueError("ambiguous truth")

    def __eq__(self, other):
        return WeirdEq.Amb()


@patch("os.path.abspath", new=WeirdEq())
def test_collect_ok():
    assert True

Run with:

PYTEST_DISABLE_PLUGIN_AUTOLOAD=1 .venv/bin/pytest --collect-only testing/test_patch_array_sentinel.py

Observed failure before the fix:

============================= test session starts ==============================
platform linux -- Python 3.8.16, pytest-5.0.2.dev58+gcb828ebe7, py-1.11.0, pluggy-0.13.1
rootdir: /workspace/pytest, inifile: tox.ini
collected 0 items / 1 errors

==================================== ERRORS ====================================
____________ ERROR collecting testing/test_patch_array_sentinel.py _____________
testing/test_patch_array_sentinel.py:7: in __bool__
    raise ValueError("ambiguous truth")
E   ValueError: ambiguous truth
=========================== short test summary info ============================
FAILED testing/test_patch_array_sentinel.py - ValueError: ambiguous truth
!!!!!!!!!!!!!!!!!!! Interrupted: 1 errors during collection !!!!!!!!!!!!!!!!!!!!
=========================== 1 error in 0.04 seconds ============================

Fix details

• num_mock_patch_args now matches sentinel replacements using is comparisons against the sentinel singletons instead of equality
• avoids executing user-defined __eq__ implementations when counting sentinel arguments, restoring safe collection

Testing

• PYTEST_DISABLE_PLUGIN_AUTOLOAD=1 .venv/bin/pytest --collect-only testing/test_patch_array_sentinel.py
• PYTEST_DISABLE_PLUGIN_AUTOLOAD=1 .venv/bin/pytest testing/test_patch_array_sentinel.py
• flake8 src/_pytest/compat.py testing/test_patch_array_sentinel.py

[casey-brooks]

Test & Lint Summary

• PYTEST_DISABLE_PLUGIN_AUTOLOAD=1 .venv/bin/pytest --collect-only testing/test_patch_array_sentinel.py (collected 1 test, 0 errors)
• PYTEST_DISABLE_PLUGIN_AUTOLOAD=1 .venv/bin/pytest testing/test_patch_array_sentinel.py (1 passed)
• flake8 src/_pytest/compat.py testing/test_patch_array_sentinel.py (no issues)

[noa-lucent]

Looks solid—thanks for the regression test.